The present invention relates to vehicles which include an internal combustion engine and, more specifically, to starters and their switching systems used with such vehicles.
Conventional internal combustion engine vehicles utilize a starter when initially starting the internal combustion engine. Typically, the battery powers an electrical starter motor which turns a flywheel and thereby turns the engine over. A solenoid is typically used to move a pinion gear into and out of engagement with a ring gear affixed to the engine's flywheel. The starter provides torque to the engine for a brief period of time until the engine starts to operate normally and no longer needs its assistance.
In a conventional vehicle, the starter will be used when initially starting the engine and the engine will continue to run until the operator intentionally stops the engine. Furthermore, many vehicles have begun employing a stop-start system where the electronic control unit of the vehicle intentionally stops the engine based upon the operating conditions of the vehicle and subsequently quickly restarts the engine based upon operating conditions of the vehicle. In many vehicles, the same starter assembly used to initially start the engine is also used when the ECU automatically restarts the engine after stopping the engine as a part of a stop-start system.
Hybrid vehicles often employ a stop-start system to temporarily stop the operation of the internal combustion engine when the vehicle is brought to a stop or when the forward propulsion of the vehicle can be entirely provided by an electric traction motor, but such stop-start systems are also used in non-hybrid vehicles which are entirely reliant upon an internal combustion engine for propulsion. In such non-hybrid vehicles, the stop-start system will typically stop engine operation when the brake is being applied and the vehicle is being brought to a stop or when the vehicle is stopped, and the internal combustion engine must be quickly restarted to resume powered vehicle movement.
In starter-based stop-start systems, the starter must restart the internal combustion engine quickly to ensure acceptable vehicle drivability characteristics, particularly in non-hybrid vehicles where the internal combustion engine is the sole propulsion power source. A stop-start system may have “change-of-mind” capabilities by which it is able to restart the engine very shortly after engine operation was stopped and the flywheel is still inertially rotating. In such starter-based stop-start systems, the starter will typically have a pinion gear that is capable of engaging a rotating ring gear that is coupled with a flywheel to thereby restart the engine. Such starters may have what is referred to as a synchronized design wherein the rotational speeds of both the pinion gear and the ring gear are sensed and the pinion gear engages the ring gear only when the speeds of the two gears are synchronized.
FIG. 1 schematically depicts vehicle 20 with starter and switch system 22. Vehicle 20 includes internal combustion engine 24 and drivetrain 26 that transmits torque from engine 24 to driven wheels 28. Although depicted vehicle 20 is a front-wheel drive passenger car, the vehicle could be of any powertrain configuration with a conventional or stop-start internal combustion engine or a hybrid powertrain. Moreover, as depicted, vehicle 20 may be a vehicle having starter and switch system 22 according to the prior art, or according to the present disclosure; a detailed description of the latter is provided further below. In other words, starter and switch system 22 is generic.
In vehicle 20, ring gear 30 is mounted on the outer circumference of a flywheel coupled to the drive shaft of engine 24. Starter and switch system 22 of vehicle 20 includes generic starter assembly 32 used to rotate the flywheel when starting engine 24. Starter assembly 32 includes electric motor 34 having a field winding, an armature or rotor, an armature shaft, a commutator, carbon brushes, a supporting frame, and a motor housing. The armature and commutator are mounted on armature shaft 36, which is coupled to pinion shaft 38 through overrunning clutch 40.
Starter motor 34 is typically a brushed DC motor and operates in a conventional manner, with the field winding forming a stationary electromagnetic field. As the armature rotates, the commutator segments contact different brushes and reverse polarity to thereby cause the continued rotation of the armature. The field and armature windings may form a series motor, a shunt motor, or a compound motor, as is well understood by those having ordinary skill in the art.
Pinion gear 42 is mounted on pinion shaft 38 of starter assembly 32, and is selectively engageable with ring gear 30. Pinion gear 42 is shifted axially with pinion shaft 38 into and out of engagement with ring gear 30 by solenoid 44 of starter assembly 32, which acts on pinion shaft 38 and pinion gear 42 through a linkage assembly that includes elongate pinion shift lever 46. A suitable source of electrical direct current, such as conventional 12V car battery 48, for example, is used to provide electrical power to starter motor 34 and solenoid 44 through the starter switch system.
It is to be noted that FIG. 1 is a schematic drawing of a generic starter and switch system that has been simplified. For example, a control circuit that includes the ignition switch of vehicle 20 and a neutral safety switch which prevents the ignition switch from activating starter motor 34 while vehicle 20 is in gear is not shown. Vehicle 20 also includes electronic control unit (“ECU”) 50 that controls the operation of starter motor 34 and solenoid 44 of starter assembly 32 by means of relays or other suitable switching mechanisms. ECU 50 receives signals indicative of vehicle system statuses, and issues corresponding control signals to effect responsive vehicle operations, or prevent certain operations, as will be readily appreciated by a person having ordinary skill in the art. Typically, starter relay switch 52 is connected to both solenoid 44 and the field winding of motor 34. An output signal of ECU 50 controls the operation of starter relay switch 52 to selectively open and close a battery circuit to energize and de-energize motor 34 and solenoid 44 of starter assembly 32.
Once engine 24 begins running, pinion gear 42 is disengaged from ring gear 30. Before disengagement of pinion gear 42, however, it is possible for the engine speed to exceed that of the armature of starter motor 34, and overrunning clutch 40 prevents damage to starter motor 34 in such a situation. Overrunning clutch 40 transmits torque from starter motor 34 to pinion gear 42 in one rotational direction, but freewheels in the opposite direction to prevent the ring gear 30 from transmitting torque to the armature of starter motor 34. Consequently, if engine 24 runs at a speed higher than that of the starter motor armature while pinion gear 42 is engaged with ring gear 30, overrunning clutch 40 will allow pinion shaft 38 and pinion gear 42 to rotate at a speed faster than that of armature shaft 36 to which the armature is rotatably fixed. The use of an overrunning clutch between a starter motor and a ring gear is known to those having ordinary skill in the art, and illustrated overrunning clutch 40 operates in a conventional manner to prevent the transmission of torque from ring gear 30 to the armature of starter motor 34.
Starter solenoid 44 includes coil 54 which, when energized, attracts solenoid plunger 56 and electromagnetically forces it axially inwardly relative to solenoid housing 55, which is affixed to the starter motor housing such that the axes of solenoid plunger 56 and armature shaft 36 are generally parallel. As mentioned above, solenoid 44 is used to shift the position of pinion gear 42 axially into and out of engagement with ring gear 30 through elongate shift lever 46. At the first of its two opposite ends, shift lever 46 is pinned to plunger 56 of solenoid 44 or to projection 58 extending from plunger 56. Plunger projection 58 may be part of spring-biased pinion engagement jump device 60 carried by solenoid plunger 56. Shift lever 46 is pivotally mounted near its midpoint to starter frame 62 and, at the second of its two opposite ends, is coupled with armature shaft 36 or pinion shaft 38 via sliding collar 63 disposed about the shaft.
Solenoid plunger 56 is biased in an axially outward direction, relative to solenoid housing 55, by compression solenoid return spring 64. As shift lever 46 is pivotably connected to starter frame 62 near its midpoint, solenoid return spring 64 biases pinion gear 42 axially inwardly towards motor 34 and into the starter's fully retracted, home position, which is shown in FIG. 1. In the starter's home position, pinion gear 42 is axially located away from ring gear 30 and cannot be enmeshed therewith. When solenoid coil 54 is energized, solenoid plunger 56 is electromagnetically pulled axially into solenoid housing 55 against the biasing force of solenoid return spring 64. Shift lever 46 is consequently urged, through pinion engagement jump device 60, to pivot about its midpoint and urge pinion gear 42, through collar 63, axially outwardly away from starter motor 34 and into the starter's extended, engagement position, in which pinion gear 42 is received into engagement with ring gear 30.
During starter engagement, when sliding collar 63 is shifted toward ring gear 30, overrunning clutch 40 and pinion gear 42 will also be shifted toward ring gear 30. If, when solenoid plunger 56 is electromagnetically pulled axially into solenoid housing 55, the teeth of pinion gear 42 do not initially mesh with the teeth of ring gear 30, jump spring 66 of pinion engagement jump device 60 will compress and exert a biasing force on sliding collar 63, through shift lever 46, that urges pinion gear 42 toward ring gear 30. Once the teeth of the pinion and ring gears are aligned to allow for their teeth to mesh, the biasing force exerted by jump spring 66 on sliding collar 63 through shift lever 46 will force pinion gear 42 into meshed engagement with ring gear 30. To similar effect, pinion engagement jump device 60 and its jump spring 66 may be alternatively located on armature shaft 36. Such use for sliding collars and/or pinion engagement jump devices having jump springs is well-known to those having ordinary skill in the art.
FIG. 1 shows solenoid plunger 56 of de-energized solenoid 44 in its extended position achieved under the influence of solenoid return spring 64, thereby forcing pinion gear 42 into the starter's fully retracted, home position wherein pinion gear 42 is axially distanced from and out of engagement with ring gear 30. When solenoid coil 54 is de-energized, solenoid plunger 56 is forced by solenoid return spring 64 axially outward, relative to solenoid housing 55, towards its extended position, thereby causing shift lever 46 to rotate about its pivot point and push sliding collar 63 towards motor 34, thereby moving pinion gear 42 out of engagement with ring gear 30 and urging pinion gear 42 into the starter's retracted, home position. In the starter's home position, a mechanical stop (not shown) on armature shaft 36 positively engages sliding collar 63 to limit its axially inward travel along the shaft towards motor 34. The axially outward travel of pinion gear 42 away from motor 34 may be similarly limited by a mechanical stop to establish the starter's fully extended, engagement position.
In the starter's engagement position, solenoid plunger 56 is located in its fully retracted position while solenoid coil 54 is energized. When solenoid plunger 56 reaches its fully retracted position, lever arm 46 has shifted pinion shaft 38 and pinion gear 42 axially outwardly away from starter motor 34, towards the starter's fully extended, engagement position wherein pinion gear 42 would be enmeshed with ring gear 30. The starter's engagement position may be entered with starter motor 34 de-energized and pinion gear 42 not rotating, as when starting a non-rotating engine 24. Alternatively, the starter's engagement position may be entered with starter motor 34 energized and pinion gear 42 being drivingly rotated, as when restarting engine 24 while its flywheel is still rotating under an inertial load. For example, in some prior starter systems, as the starter enters its engagement position to restart engine 24, the speed of the rotating pinion gear is substantially synchronized with that of the still-rotating ring gear. Regardless of whether the starter motor is rotating at the time of starter engagement, once the pinion and ring gears are enmeshed, they are sped up together as the starter cranks the engine for starting. Typically, starter cranking speed is determined by the level of power supplied to the starter motor field winding and the torque required to crank the engine. For a given power level supplied to the starter motor field winding, trade-offs occur between cranking speed and starter torque. Power, speed and torque may thus be adjusted to refine characteristics of a vehicle starter system.
For example, cold engine starts, which occur when the vehicle operator initially starts the engine, are typically under conditions of the engine oil being viscous and fuel in the cylinders being less readily vaporized than when the engine has just been operating. The engine cranks less readily during cold starts than during warm starts, and does not fire as readily. Thus, higher torque and longer cranking periods typically occur during cold starts than during warm starts. During warm starts, the engine oil is less viscous, and fuel in the engine's combustion chambers will be more readily vaporized and combusted. That relatively shorter cranking periods typically occur, and less cranking torque is required, during warm starts than cold starts is particularly desirable in vehicles having stop-start capabilities in which quick restarting is required. The starter may thus assist the restarted engine in again reaching operating speed more quickly.
For some vehicle applications, particularly those having stop-start systems, it is desirable to provide a starter and switch system 22 capable of providing variable flux to starter motor 34, by which different starter torque, speed, and power characteristics may be selected and/or obtained. Control of starter flux may be accomplished in these starter and switch systems by shorting across a portion of the starter motor field winding, and such variable flux starter and switching systems are often known as having warm-start capabilities. Generic starter assembly 32 shown in FIG. 1 may be of the variable flux type having warm start capabilities.
The operation of a variable flux starter and switch system having warm-start capabilities according to the prior art may be best understood with reference to FIGS. 2A and 2B, which schematically show prior variable flux starter and switch system 122 developed by the assignee of the present application. Elements of generic system 22 described above that are particular to system 122, are similarly represented by the sum of the corresponding generic system's element reference numeral plus 100. Below, in describing a system according to the present disclosure, elements of that system which differ from a corresponding element of prior system 122 are represented by the sum of the generic system's element reference numeral plus 200.
In prior variable flux starter and switch system 122 depicted in FIGS. 2A and 2B, ECU 150 issues separate motor activation signal 68 and desired motor flux level signal 70 at their respective terminals. The issuance of starter activation signal 68 is indicative of desired starter assembly activation. The issuance of flux level signal 70 is indicative of a desired motor flux level different from a default motor flux level, which would result in the absence of flux level signal 70. In system 122, the default motor flux level provides cold-start operation, whereas the issuance of flux level signal 70 provides warm-start operation. In response to issuance of signals 68 and 70, system 122 activates starter assembly 132, and applies a warm-start short condition over a portion of starter motor field winding 74, respectively. As discussed above, when starting engine 24, starter motor 34 is energized, and pinion gear 42 is engaged with ring gear 30 to rotate the flywheel of engine 24 attached to ring gear 30 and provide the initial torque necessary to start engine 24. FIGS. 2A and 2B both show system 122 with motor 134 and solenoid 144 of starter assembly 132 activated, a condition resulting from starter relay switch 52 receiving a starter activation signal 68 issuing from its ECU terminal, as indicated by the check mark (✓) near that terminal. In system 122, starter relay switch 52 has a 2 A coil receivable of the starter activation signal from ECU terminal 68 and is capable of switching 30 A. When activated, starter relay switch 52 energizes solenoid 144 by relaying current from battery 48 to solenoid coil 54.
FIG. 2A shows system 122 in a cold-start operating condition, with no flux level signal 70 issuing from its ECU terminal, as indicated by the X across the lead from that terminal; though here signal 70 is absent, reference numeral 70 is included to indicate in FIG. 2A the respective flux level signal terminal of ECU 150. FIG. 2B shows system 122 in a warm-start operating condition, with flux level signal 70 issuing from its ECU terminal, as indicated by the check mark (✓) near that terminal. Variable flux starter and switch system 122 is adapted to selectively short out one of first portion 74a and second portion 74b of starter motor winding 74 to increase the rotational speed of starter motor 134 for warm starts. In the examples herein described, starter motor field winding second portion 74b is selectively shorted to accomplish warm-start operation.
As warm starts generally crank the engine at a faster speed and with less cranking torque than usually necessary for cold starts, the design shown in FIGS. 2A and 2B has been found advantageous for vehicles having starter-based stop-start capabilities, wherein warm starts are desired to occur as quickly as possible. By not shorting across a portion 74a or 74b of starter motor field winding 74, i.e., by allowing rotation of its starter motor to be powered by battery current flow through its entire winding 74, as previously done in non-variable flux starters, variable flux starter assembly 132 provides high torque engine cranking performance at lower speeds, which is better suited for cold starts. Selectively shorting across portion 74a or (as depicted) portion 74b of starter motor field winding 74, however, facilitates high speed, low torque engine cranking suitable for warm starts, and is preferable for stop-start systems which require quick, repetitive engine restarting.
In prior starter and switch system 122, during both cold-start and warm-start operation starter activation signal 68 issues from ECU 150. Solenoid 144 of starter assembly 132 is energized and its plunger 156 is retracted into solenoid housing 55, moving pinion gear 42 towards the starter's extended, engagement position through shift lever 46. Starter assembly 132 includes electric motor 134 and motor energizing switch 76 for directing battery current to field winding 74 of the motor.
Motor energizing switch 76 is generally disposed within housing 55 of starter solenoid 144 and includes moveable contact plate 78 and a fixed pair of separated contact pads 80. Contact plate 78 is carried by solenoid plunger 156 and is moved into electrical engagement with contact pads 80, thereby closing switch 76 and conducting current from battery 48 through switch 76 to motor 134. Thus, with solenoid 144 energized, battery voltage is applied to starter motor field winding 74. During cold-start operation, shown in FIG. 2A, the battery current passing through motor energizing switch 76 is directed through both first portion 74a and second portion 74b of starter motor field winding 74 in series, resulting in starter motor 134 rotating with a first, low cranking speed and first, high cranking torque suitable for cold starts.
Starter and switch system 122 also includes main shorting relay switch 72 which selectively shorts out second portion 74b of starter motor field winding 74 in response to (warm-start) flux level signal 70 issuing from ECU 150. Referring to FIG. 2B, with main shorting relay switch 72 being closed in response to issuance of signal 70, the battery current passed through closed motor energizing switch 76 substantially bypasses starter motor field winding second portion 74b and is conducted through only field winding first portion 74a, resulting in starter motor 134 rotating with comparatively higher, second cranking speed and comparatively lower, second cranking torque, which is suitable for warm starts.
Under warm-start operation of prior system 122, full starter motor current travels through main shorting relay switch 72, which is therefore required to accommodate high power levels. Full starter motor current can be as high as 500 A, so main shorting switch 72 must be designed with a 30 A coil to be able to reliably selectively switch the high, 500 A motor cold cranking current. Signals from ECU 150 are typically maximized at 2 A. Therefore, intermediate or warm-start control relay switch 82 is provided electrically between ECU 150 and main shorting relay switch 72. Intermediate control relay switch 82 has a 2 A coil receivable of (warm-start) flux level signal 70 from ECU 150 and is capable of switching 30 A. Typically, the 2 A relay switches 52 and 82 both have locations in the vehicle that are remote from starter assembly 132, especially in light-duty vehicle applications. The 30 A current signal relayed by intermediate control relay switch 82 closes high power main shorting relay switch 72, which selectively applies the short across starter motor field winding second portion 74b for warm-start operation.
In prior starter and switch system 122, during cold-start operation, when no signal 70 issues from ECU 150 (as indicated by the X across the respective terminal lead), intermediate control relay switch 82 remains open, and no 30 A current signal is relayed by intermediate control relay switch 82 to high power main shorting relay switch 72, which consequently also remains open. With main shorting relay switch 72 open, battery current passing through motor energizing switch 76 during starter activation is directed through both first portion 74a and second portion 74b of starter motor field winding 74 in series, resulting in starter motor 134 rotating with its low, first cranking speed and high, first cranking torque suitable for cold starts. Starter and switch system 122 thus provides warm-start capabilities with cold-start operation by default. Notably, these relatively lower cranking speed and higher torque cold-start operating conditions can also be applied to ring gear 30 for warm starts in the event of a system or component failure that results in the short across second starter motor field winding portion 74b failing to occur as desired, providing fail-safe starter operation.
Although prior variable flux starter and switch system 122 of FIGS. 2A and 2B successfully provides warm start capabilities, a continuing goal for OEM manufacturers and their suppliers is to reduce costs, improve reliability, and minimize the package space requirements of vehicle components. A variable flux starter and switch system that advances the art toward these goals is desirable.